54,273 research outputs found
Observations of Dissipation of Slow Magneto-acoustic Waves in a Polar Coronal Hole
We focus on a polar coronal hole region to find any evidence of dissipation
of propagating slow magneto-acoustic waves. We obtained time-distance and
frequency-distance maps along the plume structure in a polar coronal hole. We
also obtained Fourier power maps of the polar coronal hole in different
frequency ranges in 171~\AA\ and 193~\AA\ passbands. We performed intensity
distribution statistics in time domain at several locations in the polar
coronal hole. We find the presence of propagating slow magneto-acoustic waves
having temperature dependent propagation speeds. The wavelet analysis and
Fourier power maps of the polar coronal hole show that low-frequency waves are
travelling longer distances (longer detection length) as compared to
high-frequency waves. We found two distinct dissipation length scales of wave
amplitude decay at two different height ranges (between 0--10 Mm and 10--70 Mm)
along the observed plume structure. The dissipation lengths obtained at higher
height range show some frequency dependence. Individual Fourier power spectrum
at several locations show a power-law distribution with frequency whereas
probability density function (PDF) of intensity fluctuations in time show
nearly Gaussian distributions. Propagating slow magneto-acoustic waves are
getting heavily damped (small dissipation lengths) within the first 10~Mm
distance. Beyond that waves are getting damped slowly with height. Frequency
dependent dissipation lengths of wave propagation at higher heights may
indicate the possibility of wave dissipation due to thermal conduction,
however, the contribution from other dissipative parameters cannot be ruled
out. Power-law distributed power spectra were also found at lower heights in
the solar corona, which may provide viable information on the generation of
longer period waves in the solar atmosphere.Comment: corrected typos and grammar, In press A&
Barrier modification in sub-barrier fusion reactions using Wong formula with Skyrme forces in semiclassical formalism
We obtain the nuclear proximity potential by using semiclassical extended
Thomas Fermi (ETF) approach in Skyrme energy density formalism (SEDF), and use
it in the extended -summed Wong formula under frozen density
approximation. This method has the advantage of allowing the use of different
Skyrme forces, giving different barriers. Thus, for a given reaction, we could
choose a Skyrme force with proper barrier characteristics, not-requiring extra
``barrier lowering" or ``barrier narrowing" for a best fit to data. For the
Ni+Mo reaction, the -summed Wong formula, with effects of
deformations and orientations of nuclei included, fits the fusion-evaporation
cross section data exactly for the force GSkI, requiring additional barrier
modifications for forces SIII and SV. However, the same for other similar
reactions, like Ni+Ni, fits the data best for SIII force.
Hence, the barrier modification effects in -summed Wong expression
depends on the choice of Skyrme force in extended ETF method.Comment: INPC2010, Vancouver, CANAD
Staggered fermion matrix elements using smeared operators
We investigate the use of two kinds of staggered fermion operators, smeared
and unsmeared. The smeared operators extend over a hypercube, and tend to
have smaller perturbative corrections than the corresponding unsmeared
operators. We use these operators to calculate kaon weak matrix elements on
quenched ensembles at , 6.2 and 6.4. Extrapolating to the continuum
limit, we find . The
systematic error is dominated by the uncertainty in the matching between
lattice and continuum operators due to the truncation of perturbation theory at
one-loop. We do not include any estimate of the errors due to quenching or to
the use of degenerate and quarks. For the
electromagnetic penguin operators we find
and . We also use the ratio of unsmeared to
smeared operators to make a partially non-perturbative estimate of the
renormalization of the quark mass for staggered fermions. We find that tadpole
improved perturbation theory works well if the coupling is chosen to be
\alpha_\MSbar(q^*=1/a).Comment: 22 pages, 1 figure, uses eps
Hinode EIS line widths in the quiet corona up to 1.5 Rsun
We present an analysis of several Hinode EIS observations of coronal line
widths in the quiet Sun, up to 1.5 Rsun radial distances. No significant
variations are found, which indicates no damping of Alfv\'en waves in the
quiescent corona.
However, the uncertainties in estimating the instrumental width mean that a
firm conclusion cannot be reached. We present a discussion of various EIS
instrumental issues and suggest that the strongest lines, from Fe XII at 193.5
and 195.1 A, have anomalous instrumental widths. We show how line widths in EIS
are uncertain when the signal is low, and that the instrumental variation along
the slit is also uncertain. We also found an anomalous decrease (up to 40%) in
the intensities of these lines in many off-limb and active region observations,
and suggest that this is due to opacity effects. We find that the most reliable
measurements are obtained from the weaker lines.Comment: Submitted to A&A, under revision - comments welcome
Sea Contributions to Spin 1/2 Baryon Structure, Magnetic Moments, and Spin Distribution
We treat the baryon as a composite system made out of a \lq\lq core" of three
quarks (as in the standard quark model) surrounded by a \lq\lq sea" (of gluons
and -pairs) which is specified by its total quantum numbers like
flavor, spin and color. Specifically, we assume the sea to be a flavor octet
with spin 0 or 1 but no color. The general wavefunction for spin 1/2 baryons
with such a sea component is given. Application to the magnetic moments is
considered. Numerical analysis shows that a scalar (spin 0) sea with an
admixture of a vector (spin 1) sea can provide very good fits to the magnetic
moment data {\em using experimental errors}. Our best fit automatically gives
for neutron beta decay in agreement with data. This fit also gives
reasonable values for the spin distributions of the proton and neutron.Comment: 24 pages, REVTEX. References modifie
Moessbauer studies in zinc-manganese ferrites for use in measuring small velocities and accelerations with great precision
Mossbauer spectroscopy was used for a systematic study of the magnetic behavior of manganese and zinc in mixed ferrites. It was observed that Zn2+ has preference to substitute Mn2+ at interstitial sites where the metal ions are tetrahedrally coordinated with four oxygen neighbors. The internal magnetic hyperfine field at the tetrahedral iron site is larger than that at the octahedral site. The relaxation effects were observed to play an important role as the zinc contents were increased, while the spin-correlation time and the magnetic field were observed to decrease in strength. It is concluded that Mossbauer effect data on complex materials, when used in conjunction with other data, can provide useful insight into the origin of the microscopic properties of magnetic materials
Dynamical cluster-decay model for hot and rotating light-mass nuclear systems, applied to low-energy S + Mg Ni reaction
The dynamical cluster-decay model (DCM) is developed further for the decay of
hot and rotating compound nuclei (CN) formed in light heavy-ion reactions. The
model is worked out in terms of only one parameter, namely the neck-length
parameter, which is related to the total kinetic energy TKE(T) or effective
Q-value at temperature T of the hot CN, defined in terms of the
both the light-particles (LP), with 4, Z 2, as well as the
complex intermediate mass fragments (IMF), with , is
considered as the dynamical collective mass motion of preformed clusters
through the barrier. Within the same dynamical model treatment, the LPs are
shown to have different characteristics as compared to the IMFs. The systematic
variation of the LP emission cross section , and IMF emission
cross section , calculated on the present DCM match exactly the
statistical fission model predictions. It is for the first time that a
non-statistical dynamical description is developed for the emission of
light-particles from the hot and rotating CN. The model is applied to the decay
of Ni formed in the S + Mg reaction at two incident
energies E = 51.6 and 60.5 MeV. Both the IMFs and average
spectra are found to compare reasonably nicely with the experimental data,
favoring asymmetric mass distributions. The LPs emission cross section is shown
to depend strongly on the type of emitted particles and their multiplicities
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